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  Adaptive predistortion for controlling an open loop power amplifierUSPTO Application #: 20080051042Title: Adaptive predistortion for controlling an open loop power amplifier Abstract: An adaptive predistortion system for controlling an open loop power amplifier includes a transmitter, a receiver, a phase and amplitude determination element configured to determine amplitude and phase characteristics of an output signal generated in the transmitter, the signal representing transmitter characteristics, an amplitude resampling element configured to generate an updated AM-AM predistortion signal based on the output signal generated in the transmitter, and an amplitude predistortion element configured to compare the updated AM-AM predistortion signal with a factory-calibrated AM-AM predistortion signal and generate an amplitude compensation signal. The adaptive predistortion system also includes a phase comparison element configured to compare the signal representing transmitter characteristics with a desired phase signal, a phase resampling element configured to generate an updated AM-PM predistortion signal based on the output signal generated in the transmitter, and a phase predistortion element configured to compare the updated AM-PM predistortion signal with a factory-calibrated AM-PM predistortion signal and generate a phase compensation signal. (end of abstract)
Agent: Smith Frohwein Tempel Greenlee Blaha, LLC - Atlanta, GA, US Inventors: Jaleh Komaili, John E. Vasa, Morten Damgaard, David S. Ripley USPTO Applicaton #: 20080051042 - Class: 4551143 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080051042. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]Radio frequency (RF) transmitters are found in many one-way and two-way communication devices, such as portable communication devices, (cellular telephones), personal digital assistants (PDAs) and other communication devices. An RF transmitter must transmit using whatever communication methodology is dictated by the particular communication system within which it is operating. For example, communication methodologies typically include amplitude modulation, frequency modulation, phase modulation, or a combination of these. In a typical GSM mobile communication system using narrowband TDMA technology, a GMSK/8-PSK modulation scheme supplies a low noise phase modulated (PM) transmit signal to a non-linear power amplifier directly from an oscillator. [0002]Typically, the power output of a power amplifier is controlled using either closed-loop methodology or an open-loop methodology. In a closed-loop power control system, a portion of the output of the power amplifier is diverted to closed-loop power control circuitry associated with the power amplifier. The closed-loop power control circuitry analyzes a number of factors, including a power control signal generated in the device and the power output of the power amplifier, and determines the optimal desired power to be output from the power amplifier. The closed-loop power control circuitry then delivers a power control signal to the power amplifier to control the power amplifier power output. Unfortunately, a closed-loop power control system requires costly components and consumes valuable space on the device in which the transmitter is fabricated. [0003]Open power control systems have been implemented in an effort to reduce the cost associated with a closed-loop power control system. In an open loop power control system, power amplifier non-linearities are estimated during manufacturing and the inverse of those estimates are applied to the power amplifier as pre-distortion during normal operating conditions. The pre-distortion settings are developed from compensation curves that are generated as a result of the factory-estimated non-linearities. As long as the power amplifier characteristics remain stable, such an approach provides acceptable results. However, while some power amplifier sub-systems may remain stable over time, temperature variations, aging, etc., there are other operating conditions that can alter the response of the power amplifier. For example, a change in the voltage standing wave ratio (VSWR) at the power amplifier output can alter the operating parameters (and response) of the power amplifier for a period of time sufficient to cause transmission failures. This occurs when the power amplifier encounters an operating condition for which the compensation curves that are generated as a result of the factory-estimated non-linearities no longer apply. Open loop power control systems are vulnerable to such conditions. [0004]Therefore, it would be desirable to overcome such operating limitations. SUMMARY [0005]Embodiments of the invention include an adaptive predistortion system for controlling an open loop power amplifier including a transmitter, a receiver, a phase and amplitude determination element configured to determine amplitude and phase characteristics of an output signal generated in the transmitter, the signal representing transmitter characteristics, an amplitude resampling element configured to generate an updated AM-AM predistortion signal based on the output signal generated in the transmitter, and an amplitude predistortion element configured to compare the updated AM-AM predistortion signal with a factory-calibrated AM-AM predistortion signal and generate an amplitude compensation signal. The adaptive predistortion system also includes a phase comparison element configured to compare the signal representing transmitter characteristics with a desired phase signal, a phase resampling element configured to generate an updated AM-PM predistortion signal based on the output signal generated in the transmitter, and a phase predistortion element configured to compare the updated AM-PM predistortion signal with a factory-calibrated AM-PM predistortion signal and generate a phase compensation signal. [0006]Related methods of operation are also provided. Other systems, methods, features, and advantages of the invention will be or become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. BRIEF DESCRIPTION OF THE FIGURES [0007]The invention can be better understood with reference to the following figures. The components within the figures are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. [0008]FIG. 1 is a block diagram illustrating a simplified portable transceiver. [0009]FIG. 2 is a block diagram illustrating an open-loop polar RF transmitter and a portion of a receiver in accordance with an embodiment of the invention. [0010]FIG. 3 is a graphical illustration showing an 8-PSK time mask and power signal showing the time period during which embodiments of the invention are implemented. [0011]FIG. 4 is a graphical illustration showing an example of AM-AM power amplifier distortion curves showing a factory calibration curve and an estimated curve. [0012]FIG. 5 is a graphical illustration showing an example of AM-PM power amplifier distortion curves showing a factory calibration curve and an estimated curve. [0013]FIG. 6 is a flowchart showing the operation of an embodiment of the adaptive predistortion system and method. DETAILED DESCRIPTION [0014]Although described with particular reference to a portable transceiver, the adaptive predistortion system and method for controlling an open loop power amplifier can be implemented in any system in which a transmitted signal includes both an AM component and a PM component, and in which the AM component is applied to the control port of the power amplifier. [0015]The adaptive predistortion system and method for controlling an open loop power amplifier can be implemented in hardware, software, or a combination of hardware and software. When implemented in hardware, the adaptive predistortion system and method for controlling an open loop power amplifier can be implemented using specialized hardware elements and logic. When the adaptive predistortion system and method for controlling an open loop power amplifier is implemented partially in software, the software portion can be used to adaptively apply estimated AM and PM pre-distortion characteristics to the transmitter, thereby compensating for the AM and PM characteristics during normal use of the transmitter, if these characteristics should change as a function of temperature, aging, VSWR or other factors. The software can be stored in a memory and executed by a suitable instruction execution system (microprocessor). The hardware implementation of the adaptive predistortion system and method for controlling an open loop power amplifier can include any or a combination of the following technologies, which are all well known in the art: discrete electronic components, a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit having appropriate logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. [0016]The software for the adaptive predistortion system and method for controlling an open loop power amplifier comprises an ordered listing of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. [0017]In the context of this document, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory) (magnetic), an optical fiber (optical), and a portable compact disc read-only memory (CDROM) (optical). Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance, optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory. [0018]FIG. 1 is a block diagram illustrating a simplified portable transceiver 100. The portable transceiver 100 includes speaker 102, display 104, keyboard 106, and microphone 108, all connected to baseband subsystem 110. In a particular embodiment, the portable transceiver 100 can be, for example but not limited to, a portable telecommunication handset such as a mobile cellular-type telephone. The speaker 102 and the display 104 receive signals from the baseband subsystem 110 via connections 112 and 114, respectively, as known to those skilled in the art. Similarly, the keyboard 106 and the microphone 108 supply signals to the baseband subsystem 110 via connections 116 and 118, respectively. The baseband subsystem 110 includes microprocessor (.mu.P) 120, memory 122, analog circuitry 124, and digital signal processor (DSP) 126 in communication via bus 128. The bus 128, though shown as a single bus, may be implemented using a number of busses connected as appropriate among the subsystems within baseband subsystem 110. The microprocessor 120 and the memory 122 provide the signal timing, processing and storage functions for the portable transceiver 100. If portions of the adaptive predistortion system and method for controlling an open loop power amplifier are implemented in software, then the memory 122 also includes power amplifier pre-distortion software 355 that can be executed by the microprocessor 120, the DSP 126 or by another processor, and compensation tables 360 that are developed based on the performance of the transmitter 200 and used to compensate for non-linearities in the power amplifier, to be described below. [0019]The analog circuitry 124 provides the analog processing functions for the signals within the baseband subsystem 110. The baseband subsystem 110 communicates with the radio frequency (RF)/mixed signal device (MSD) subsystem 130 via the bus 128. [0020]The RF/MSD subsystem 130 includes both analog and digital components. For example, the RF/MSD subsystem 130 includes a transmitter 200, a receiver 170, an analog-to-digital converter 134, and one or more analog-to-digital converters (DAC). In this embodiment, the transmitter 200 includes a DAC 144. The DAC 144 processes the digital transmit data to be supplied to the modulator 146. Continue reading... Full patent description for Adaptive predistortion for controlling an open loop power amplifier Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Adaptive predistortion for controlling an open loop power amplifier patent application. Patent Applications in related categories: 20080233902 - Method and apparatus for communicating precoding or beamforming information to users in mimo wireless communication systems - Methods and apparatus for communicating precoding or beamforming information to users are disclosed. A feedback signal including a reported preceding matrix index (PMI) is received and a determination made as to the state of the feedback. 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